First Airborne Thermal Infrared Hyperspectral Imaging of a Dry Lake: Real- World Data and Tes/themis Mars Interpretations

Researchers seek to identify dry lake bed deposits on Mars, if present. The Global Surveyor TES and Mars Odyssey THEMIS are primary tools in this search. However, there are no published thermal infrared spectrometer (hyperspectral) airborne studies of a dry lake bed. Here we present the first such study and the impacts on TES/THEMIS interpretations. This research addresses a looming gap in the field spectroscopy experience required for complete and rigorous interpretations of TES/THEMIS data. A companion abstract focuses on the relevant Bristol Lake geology [1]. A hallmark of this work is the alliance of field geologists and field spectroscopists. Background: Past thermal infrared terrestrial analog remote sensing studies used multi-channel radiometer data (e.g., TIMS, MASTER), because airborne hyperspectral (spectrometer) thermal emission data sets were not available. Kirkland et al. published the first geologic study that used an airborne thermal infrared hyperspectral imager [2]. The study uncovered key spectral effects that occur in the field and that alter TES interpretations, with a focus variations on carbonate textures. Here we extend this first-ever style of fundamental study to cover a dry lake bed (playa). Site: Bristol Lake is in the Mojave desert, near Amboy. Fig. 1 shows the site studied. Geologic units along the SEBASS line from [3] are: Qpsh: Silt, clay, and halite salt (Holocene). Qpsg: Silt, clay, gypsum, and celestite (Holocene) Qps: Silt and clay (Holocene). Qya: Alluvium. Sand and poorly sorted sandy gravel. Instruments: TES hyperspectral (spectrometer) data cover ~6.5–50 μm in 143 channels. In contrast, the supporting terrestrial airborne studies used multichannel radiometer (multi-spectral) data, mainly the Thermal Infrared Multispectral Scanner (TIMS, 6 bands), or MASTER (10 bands). THEMIS is also a multi-channel radiometer (multi-spectral, 9 bands). We analyzed unique hyperspectral (spectrometer) images recorded by the Spatially Enhanced Broadband Array Spectrograph System (SEBASS, 7.6–13.5 μm, 1321-740 cm, 128 channels) [2, 4]. Terrestrial atmospheric water vapor and CO2 absorptions limit this terrestrial atmospheric window to ~8–13 μm. SEBASS covers this full range. Multi-channel radiometer studies leave some aspects of field studies incomplete, because they lack the spectral resolution required to research detailed spectral behavior. Our studies address this gap by moving fundamental research from the laboratory to the airborne/satellite remote sensing perspective. SEBASS measures with the highest combined spectral resolution and sensitivity (signal-to-noise ratio) of any airborne thermal infrared hyperspectral imager. Fig. 2 shows the signal-to-noise ratio. Additional SEBASS information is in [2, 4].